small study conducted by the Centers for Disease
Control and Prevention has found that this season's influenza vaccine
failed to protect against the Fujian strain that has caused most cases.
Depending on the way the data were analyzed, the vaccine protected zero
to 14 percent of participants in the study, said a scientist briefed on
the study who would not allow his name to be used.
Officials of the centers said last night that they hoped that
continuing studies to be completed in the spring would show that the
vaccine offered more protection than this study indicated.
Officials had warned that there was a mismatch between the current
vaccine and the Fujian strain of influenza virus that was causing most
illness this season. But they said the vaccine should still offer some
protection to many people.
Officials of the centers discussed the findings with dozens of
influenza experts yesterday in a teleconference in advance of the study's
publication in today's issue of the agency's Morbidity and Mortality
Weekly Report.
The scientist who was briefed on the findings cautioned against drawing
conclusions from the study because of serious flaws in its design. The
findings may be countered by reports of other comprehensive studies later,
the scientist said.
This study was the first that the centers had conducted in the middle
of a flu epidemic. It involved a questionnaire sent to 3,100 health
workers at Children's Hospital in Denver, asking whether they had been
vaccinated, when and whether they developed an illness compatible with
influenza.
The study was carried out in the five weeks when influenza hit hardest
in Denver, from late October through late November. Colorado, like other
areas of the United States, experienced an onset of the influenza season
earlier than usual.
Because just 61 percent of health workers responded, and many other
infectious agents can cause flulike symptoms, experts said the study had
limitations.
An additional weakness is that epidemiologists did not take specimens
from the respondents for laboratory tests to determine what proportion of
the reported illness was actually from the influenza virus.
At meetings last February and March where experts made educated guesses
about what strains to use in preparing this season's vaccine, the panel
members knew about the new Fujian strain. But it was too late to include
it in the vaccine manufactured for the Northern Hemisphere. The vaccine
being prepared for the Southern Hemisphere is formulated to protect
against the Fujian strain.
The Denver study is the first of many that the disease control centers
and other scientists have undertaken.
"It is the first bite out of the apple, but it has left a bit of a sour
taste," said the expert, who was referring to the findings of a low level
of protection against Fujian.
The effectiveness rates of influenza vaccine vary in part according to
the age and health status of the individual. Influenza vaccine prevents
illness in about 80 percent of children and young adults. The vaccine is
less effective in preventing symptoms among those 65 and older, but
prevents major complications like pneumonia in about 70 percent of those
who receive it in the older population.
